With the current popularity of quick lubrication type services and the current emphasis on effective vehicle maintenance by the public, there has been an increasing market for the periodic changing the fluid in vehicular power steering systems as a regular maintenance procedure. A number of power steering fluid exchangers are currently being manufactured, but the need remains for an automatic power steering fluid exchanger which has all of the following desirable characteristics: the exchanger does not require connection to a vehicle's electrical system or other source of electrical power or to a compressed air supply; the fluid exchanger has the power needed for the exchange provided by either the positive and negative pressures of the power steering pump and/or provided by the exchanger's own battery power; the fluid exchanger is compact, lightweight, portable, easy to position, simple to connect, and easy to operate; the fluid exchanger is able to automatically exchange its fresh fluid for the power steering system's used fluid in approximately equivalent volumes and rates of flow; the fluid exchanger automatically and reliably establishes a closed fluid circulation circuit between the inlet port and the outlet port of the power steering pump at the completion of the fluid exchange and maintains it until the service equipment operator turns off the vehicle's engine.
Fluid exchange units for power steering currently available to vehicular service centers typically consist of two categories of units, the small and portable inexpensive units and the larger much more expensive units. The units in the first category are at the lower end of the expense continuum and are small, compact toolbox sized units which can be placed on the fender or engine of the vehicle for service use. These small, compact units typically consist of two electric pumps connected to the vehicle's battery and which are simultaneously operated to extract used fluid from the reservoir of the power steering system while also injecting fresh fluid into that reservoir to replace it. This simultaneous injection of fresh fluid and extraction of used fluid is instituted through the fill cap/dipstick opening of the power steering fluid reservoir after the reservoir cap is removed and with the engine idling to make the power steering unit operative.
This first category of units have been disclosed in the Knorr in U.S. Pat. No. 5,415,247 and by Dixon in U.S. Pat. No. 6,035,902. Both feature two electrically operated pumps, each of which is connected to an associated fluid delivery hose, with one hose-pump combination conducting fresh fluid into the power steering reservoir and the other hose-pump combination extracting used fluid out of the power steering reservoir. During the fluid exchange both conduits are placed inside the reservoir at different levels and both pumps are operated simultaneously. This type of unit is compact and easy to position but because it is manually operated it must be closely monitored to prevent air infusion into the power steering system upon depletion of the fresh fluid supply. A significant drawback of this type of unit is the need to connect the unit to the vehicle's electrical system. Another drawback is its concurrent mixing of fresh fluid with contaminated used fluid in the power steering reservoir right before it is delivered to the low pressure port of the power steering pump. This tends to result in an incomplete fluid exchange typically characterized by a correspondingly lower proportion of fresh fluid exchanged for the used fluid in the circuit, compared to the second category of power steering fluid exchange units which are much more expensive and, if used properly, typically exchange a higher percentage of the used fluid for fresh. Therefore, the units of the first category, best described as “mixing type” units are only minimally effective and of limited suitability for periodic fluid exchange maintenance of power steering systems when compared to larger, more expensive units.
The units of the second category, larger and more expensive, are therefore more desirable than the small mixing type units due to their higher effectiveness in exchanging fluid. However, their higher price is a drawback which can make them less available to vehicular service centers with limited funds for service equipment acquisitions. An additional drawback is that units of this second category tend to be significantly larger, heavier, less portable and therefore less convenient to operate than the smaller, compact and much less expensive units described above to be in the first category. This second category of units includes a power steering fluid exchanger disclosed by Dixon et al in U.S. Pat. Nos. 5,806,629 and 5,583,068. This unit is connected to communicate fluidly with the power steering system's low side positive pressure discharge hose to receive used fluid there from, and is connected to communicate with the power steering pump's negative pressure or suction hose to deliver fresh fluid thereto. In order for the fluid exchange to be instituted this device must be connected to the vehicle's battery so that the unit can be activated by the operator closing an electrical switch to institute the fluid exchange which is a drawback. This unit, as do all the units in this second category of units, requires its own onboard pump to deliver fresh fluid into the power steering system. In this example, the Dixon et al device uses the used fluid flow from the pump of the power steering system to power the onboard fresh fluid pump. The need for a power steering fluid exchanger to have its own onboard pump adds significantly to the cost of the unit.
In the power steering fluid changer depicted in U.S. Pat. Nos. 5,806,629 and 5,583,068, the most important function is to provide a pumping means which controls both the used fluid flow and the fresh fluid flow to be approximately equivalent in rate and volume. In these patents, the power steering fluid changer uses a positive displacement fresh fluid pump which is powered by the discharge pressure of the pump of the power steering system. Harnessing the used fluid flow from a vehicular hydraulic circuit's own pump to power a fluid exchanger's fresh fluid positive displacement pump was a novel concept first disclosed by Viken in U.S. Pat. No. 5,318,080 which related to exchanging the fluid of an automatic transmission. Power steering system fluid exchange units based on this principal are typically expensive not only because of the size of the case required, but their complexity makes the cost of manufacturing an exchanger with a positive displacement fresh fluid pump which harnesses the power of the power steering pump quite substantial. When the unit's fresh fluid supply in the power steering fluid changer depicted in U.S. Pat. Nos. 5,806,629 and 5,583,068, becomes depleted, an electrical float switch opens which then in turn deactivates the electrical solenoid of a three-way hydraulic valve to stop the fluid exchange and to shift the unit back to its original flush mode of operation which is a default closed loop circulation allowing the pump of the power steering system to circulate fluid from its discharge port back to its inlet port. Also disclosed in the Dixon et al U.S. Pat. No. 5,806,629 is a suggestion for an alternative embodiment which requires no electrical power for its operation by replacing the solenoid operated valve with a manually actuated valve that requires close operator attention to manually revert the machine from exchange mode to flush mode when delivery of the new ATF into the transmission is completed. It is also suggested that the manually actuated three-way valve can be spring loaded and manually latched into place by the service technician to remain in its exchange-mode position until a dropping float could then release a triggering device to release the spring loaded three way valve to return under spring power to its default flush mode of operation. Dixon et neither suggested or disclosed the use a three-way valve that is directly and responsively controlled by an attached float as it freely rises or falls in the fresh fluid reservoir in response to the fluid level as is disclosed in the preferred embodiment of this instant invention.
The devices of this second category, the larger more expensive units that actually exchange fluid without just mixing it in the power steering reservoir, are expensive to manufacture because they require costly electric solenoid operated valves which need electrical power. The need remains for a small, compact, lightweight, easily portable power steering fluid exchanger which does not require electrical power, does not require one or more of its own fresh fluid delivery pump(s) to operate, and does not require a costly automatic fluid flow control mechanism to approximately match the fresh and used fluid flow rates and volumes.
Both the first and second categories of devices, the less expensive and the more expensive, typically require connection to the vehicle's battery or electrical system in order to operate. It is desirable for a service center to acquire a power steering fluid exchanger which does not require connection to the vehicle's electrical system for a number of reasons. First, having to make connection to vehicle's battery requires the use of connection wires which can make contact with moving parts in the engine compartment if wrongly positioned or moved during the fluid exchange. Second, many currently manufactured vehicles have sophisticated onboard diagnostic computer systems (OBD systems) which can sense voltage changes, voltage spikes, and anomalies in the vehicle's electric system and which will then record a fault code. If the exchanger's wires are not securely connected to the battery or electrical system of the vehicle a spark may be generated or if a short develops in the exchanger's wiring, either of these occurrences can trigger a warning code in the vehicle's computer which may result in the vehicle's computer directing the vehicle to operate in a special default mode. There have been articles published in the automotive trade literature predicting that vehicles manufactured in the future will be increasingly dependent on even more sophisticated onboard diagnostic computer systems (OBD systems). It is expected that these advanced OBD systems may be increasingly sensitive to unnecessary, non-operational current fluctuations, which may cause false error codes or cause the vehicle to assume a default mode of operation which lowers the gas mileage of the vehicle until the computer system is reset, which typically requires the vehicle to be driven for a period of time. For example, some Chrysler OBD systems are so sensitive that if a single spark plug or spark plug wire fails, the vehicle will be placed in a default operational mode with the automatic transmission operable in second gear only. Third, there have articles published in the automotive trade literature which predict that in the not too distant future automotive manufacturers will likely utilize new, higher voltage systems accompanied by newly designed high output combination alternator/starters and electrically powered air conditioners, brakes and/or suspensions. If these expected voltage increases are implemented service equipment which has been manufactured for 12 volts direct current (DC) will become obsolete and unusable unless it is modified to accept these higher voltages. If it has to be modified or replaced this will be an added and undesirable expense.
Another type of power steering fluid changer which has been available in the past has been the unit depicted by Baylor et al in U.S. Pat. No. 5,015,301. This device is operated with the vehicle's engine off and the power steering pump inoperative. This device consists of a tank with a bladder type “pusher” which holds fresh fluid on the top side and receives compressed air as a powering medium on the lower side. The need for access to shop air can limit the service area used to provide the fluid exchange. Once this device of Baylor et al is connected to the power steering system, compressed air is then provided to the lower side of the diaphragm “pusher” to pressurize the fresh fluid to flow into and through the low pressure inlet hose (or conduit) of the power steering pump to then flow through the rest of the power steering system and then finally out of the low pressure reservoir return hose (or conduit) to the unit's open used fluid receiver.
The Baylor et al patent shows only a remotely arranged reservoir style power steering system in its figures and apparently neglects to illustrate, describe and explain how the unit would be specifically connected to service the more traditional type of power steering system which has a combination reservoir/pump assembly. The Baylor et al patent teaches that this unit is operated only with the engine of the vehicle off and the pump of the power steering system not operating. The unit is normally operated in two separate procedures, the first time to infuse a fresh flushing mixture into the power steering system. The unit is then disconnected temporarily while the vehicle's engine is run for awhile to therefore circulate the fluid flushing mixture through the power steering system to dissolve varnish buildup and contaminants. The engine is then turned off and the unit is reconnected and operated a second time to flush the power steering system, this time only using fresh power steering fluid with perhaps an additive package. This particular unit is somewhat bulky and cumbersome to use, and due to the multiple steps involved, takes an unnecessarily long time to operate. In addition it seems likely that the use of such a flushing procedure without the power steering pump operative would not be as effective in removing all the used fluid as would a fluid exchange procedure accomplished with the power steering pump operative. These drawbacks prevent it from being a preferred option for those service centers who want a unit that is compact, self contained with no need for compressed shop air or connection to a source of electrical power, simple to operate and capable of exchanging a high proportion of used fluid for fresh fluid in a relatively short period of time while the power steering pump is operative.
The Graham U.S. Pat. No. 5,971,021 discloses a method for filling a new and empty power steering system or other hydraulic circuit with fresh fluid by using a specialized valve. Graham also suggests that this method can be used to exchange used fluid for fresh fluid as a maintenance procedure. It is not known if this product is commercially available at this time. This patent appears to teach the connection of a specially designed valve device midstream into the high pressure conduit of a fluid system, such as a power steering system or cooling system for the purpose of filling that fluid system for the first time. This methods teaches pressurizing a fluid and then injecting that pressurized fluid through this specialized valve which has been installed into a two sided conduit. A substantially unidirectional flow pattern through a selected side of the intercepted conduit is established by injecting most of that pressurized fluid through the valve into that selected side of the intercepted conduit while allowing a small portion of that pressurized fresh fluid to be injected into the other side of that conduit by leaking around the slide of the specialized valve. As the pressurized fresh fluid is injected into the power steering system air contained in the system is also simultaneously driven out. This valve and its use are depicted as being particularly applicable to power steering fluid systems and one figure illustrates this valve as being interconnected to such a system between the power steering pump and “gearbox” midstream in the pump's high pressure outlet conduit, with the valve arranged to discharge its pressurized fluid in a substantially unidirectional flow in the direction of the conduit which leads to the gearbox.
After this valve is properly connected to a new but empty power steering system, a pre-pressurized source of fresh fluid is then connected to this valve which in turn causes the valve to operate to inject pressurized fresh power steering fluid in a substantially unidirectional flow to fill the system and to displace air out of the system, with the capability of simultaneously allowing some fluid to also be infused upstream, thus displacing the air from two directions. This pressurized fresh fluid remains pressurized as it flows into and through the steering mechanism.
It is also taught that this valve may be connected to a used power steering system which is filled with used fluid for the purpose of exchanging its used fluid for fresh fluid as a maintenance procedure. Installing this valve as depicted for routine power steering fluid exchanges would be somewhat difficult task in and of itself due to the tendency for the power steering pump's high pressure conduit (or hose) to have connections which are often be corroded and typically somewhat difficult to reach and disconnect.
It appears that no mention is made of whether the vehicle's engine is operative while the procedure is enacted. However, the suggested positioning at which the valve is connected as apparently disclosed in Graham's patent is downstream from the pump's outlet port, and therefore it is assumed that the power steering system must be inoperative while a new fluid fill or a fluid exchange is instituted, since operating the pump with the valve downstream would obstruct the output flow of the pump and perhaps could damage the power steering pump if it's relief valve was malfunctioning or its setting was too high. Unless the valve was purchased by customer and permanently installed, at each fluid exchange service, the valve would have to be installed and used after disconnecting the power steering systems' high pressure hose (conduit). After the fluid exchange was completed the high pressure line would have to be disconnected from the valve and reconnected in its proper configuration to the power steering pump. It appears then that use of this valve and method would be too slow and unduly cumbersome to be practical for use at most vehicle service centers as a regular power steering maintenance procedure.
The Sangret U.S. Pat. No. 5,664,416 discloses a new and improved method for filling a new power steering assembly with fluid for the first time on an auto assembly line. This patent discloses a method for pumping fluid from a bulk holding tank into the power steering system's reservoir to circulate in the power steering system with the engine operative under power of the power steering pump, after which that fluid is then discharged and returned to the bulk holding tank for redundant circulation back into and through the power steering system. When a new power steering system is filled for the first time air typically becomes entrained in the power steering fluid and this method offers a solution for remove that entrained air. The patent discloses that air entrained in a power steering system may cause unwanted noise and/or vibration which may be annoying to the driver who first operates the vehicle after the filling of the power steering system.
This method teaches that redundant circulation of fluid in and out of the bulk holding tank is instituted until the power steering system is completely filled with fluid and the entrained air has been removed. This method teaches the placing of a special connector assembly in the filler opening of a certain very select configuration of remotely arranged power steering reservoir, a reservoir which has its low pressure fluid return port directly placed below and on center of the filler neck of the reservoir. This connector assembly takes the position of the reservoir cap type and has both a fresh fluid delivery conduit and a used fluid receiving or discharge conduit passing through it into the filler opening of this select type of remote power steering system reservoir. This adapter is pushed into the filler neck of the reservoir which inserts its used fluid receiving conduit matingly down and into the used fluid return port of the reservoir which is directly below and on center to the filler neck of the reservoir. This used fluid receiving conduit then receives fluid which is discharged from the power steering pump being returned to the reservoir. The fresh fluid delivery conduit of the connector assembly is shorter than the discharge conduit and does not connect with the supply conduit port of the reservoir which is located off center of the reservoir, but it discharges fresh fluid into the reservoir after being pumped out of a bulk holding tank which is sealed and provided with a vacuum pump for extracting entrained air out of the fluid. The holding tank is shown with its own fresh fluid delivery pump for delivery fresh fluid through the special adapter into the power steering reservoir. The patent does not disclose using the power steering pump's low pressure inlet port side or its positive pressure outlet side for powering the pumping of fluid into and through the power steering system redundantly, even though the engine is running to render the power steering pump operative.
The fluid discharged by the pump is then delivered through the connector assembly and into the bulk holding tank which is actually a large additional fluid reservoir which both provides supply fluid for delivery into the power steering system and receives the fluid discharged from the power steering system. The method does not disclose or teach the exchange of used fluid for fresh fluid and is apparently limited to charging a power steering system for the first time while removing the air that inevitably becomes entrained.
The method of Sangret discloses an arrangement of one electrically operated valve and two electrically operated pumps which are simultaneously activated by an electronic control unit which energizes an inductive coil when the vehicle's engine is started. The valve is a flow control valve which stops fluid flow out of the bulk holding tank when the engine is turned off which inactivates the valve, and allows fluid flow out of the bulk holding tank and into the power steering reservoir when activated by the engine running. One pump is a vacuum pump which is connected to a port near the top of the bulk tank and provides enough low pressure to evacuate any air which has become entrained in the power steering fluid after it returns to the holding tank as the power steering system is filled for the first time. The other pump is a fluid delivery pump, referred to as a flow charge pump, which when activated by the electronic control unit will pump fluid from the bulk holding tank into the power steering reservoir where the low pressure provided by the power steering pump then delivers that fluid into the conduit supplying the power steering pump.
The flow charge pump appears to be necessary for two reasons. First, the patent depicts the fluid supply port at the bottom of the bulk holding tank to be at a level below that of the connector assembly, and the negative pressure provided by the power steering pump is not likely to be great enough to pump the fluid from the bulk holding tank without assistance by an auxiliary pump. Second, the low pressure provided by the vacuum pump will likely conflict with the low pressure provided by the power steering pump which would inhibit the flow of the fresh fluid into the conduit supplying the power steering pump. The special connector assembly which is inserted into the filler neck of the power steering reservoir is shown to have a set of three O'rings for sealing but is not shown to have a positively engaging set of tab locks like many power steering caps. It can be assumed that the connector is held in place only by sidewall friction between the cap, its O'rings and the filler neck of the reservoir and any low pressure provided by the power steering pump through that pump's inlet port. One potential drawback to the use of this method of filling a new power steering system with fresh fluid for the first time is that the flow charge pump must have a delivery output pressure great enough to overcome the low pressure provided by the vacuum pump but not so great as to deliver fluid at a greater flow rate to the reservoir than the power steering pump will accept it. If this occurs pressure can build up inside the reservoir which can disrupt the sealing of the connector into the reservoir filler neck and perhaps can cause leakage of fluid and displacement of the connector up and out of position in the filler neck.
The Brown U.S. Pat. No. 5,291,968 discloses an “Apparatus and Method for Changing Automatic Transmission Fluid in Motor Vehicles” and does not address changing fluid in power steering systems. It discloses the method of removing the pan of a transmission to access the intake port of the suction conduit of the transmission pump to then connect a pressurized fresh fluid supply to that intake port while idling the engine to operate the transmission and while providing a pan underneath the transmission to receive the fluid discharged from the transmission's pump. Because the fresh fluid reservoir of the apparatus is at floor level, and since the low pressure provided by the transmission's pump is inadequate to deliver the fresh fluid from floor level up and into to the port of that suction conduit and into the transmission, the unit requires its own on-board pump to deliver fresh fluid up to the port of the suction conduit of the transmission pump.
In addition, this method apparently requires close monitoring by the operator since the engine must be turned off as soon as the fresh fluid supply of the fluid exchanger is depleted to prevent air from being pumped into the transmission.
The Matta U.S. Pat. No. 4,342,328 depicts a two stage float valve which is connected to a suction tube. The purpose of this float valve is to close off a fuel tank from the suction tube when the fuel tank starts to run dry and fuel is being drawn from another tank. This float valve is configured to be resistant to closing prematurely from the effect of the suction provided by the suction tube. This is accomplished by providing an inner poppet which equalizes the negative pressure of the suction tube to both sides of the valve's primary seal thereby neutralizing the effects of the suction on the valve's primary seal. This allows the use of a smaller float than would otherwise be necessary and prevents the negative pressure provided from the suction tube from adversely affecting the operation of the valve. This patent disclosed the problem of establishing an air tight seal when a fluid supply is diminished and the importance of preventing low pressure or suction from prematurely closing the valve. The float valve disclosed in this patent by Matta is a fluid supply valve only and does not control any exchange of fluids.
The Colvin, et al. U.S. Pat. No. 6,477,886 discloses a test apparatus for measuring the amount of air entrained in the fluid of a power steering system. The apparatus also includes a vacuum pump for drawing air out of the power steering pump. It disclosed that air and other gases entrained in the power steering fluid may result in excessive noise during the operation of the pump and may include whining and hissing, and that these noises may be similar to noises caused by improperly functioning components. It is disclosed that it is useful to be able to use a measurement device to indicate if entrained air is significant enough to be causing such noises or if not that the power steering system is damaged. This lends further credence to the importance of not allowing air to become entrained by a power steering fluid exchanger when exchanging the fluid of a power steering system since it may mask the sounds created by damaged components.